1. Field of the Invention
This invention relates to a single-use syringe for injecting medicine into a patient. More particularly, the invention relates to a safety syringe having a retractable needle cannula that renders the needle cannula harmless after it is used.
2. Background of the Related Art
Many communicable diseases can be spread through the penetration or scratching of the skin by a needle that was previously used by another having the disease. Spreading of the disease in this manner may occur by accident, such as with medical personnel making injections, or it may occur through misuse, such as by intravenous drug users using a previously used needle cannula.
Various syringes have been invented, designed and developed to retract the needle into the syringe or the plunger inside of the syringe. Some of these devices are U.S. Pat. No. 4,973,316 (Dysarz), U.S. Pat. No. 4,978,343 (Dysarz), U.S. Pat. No. 5,180,369 (Dysarz), U.S. Pat. No. 5,267,961 (Shaw), U.S. Pat. No. 5,019,044 (Tsao), U.S. Pat. No. 5,084,018 (Tsao), U.S. Pat. No. 5,385,551 (Shaw), U.S. Pat. No. 5,389,076 (Shaw), and U.S. Pat. No. 5,201,710 (Caselli). These designs have needles which retract at the end of the injection. Most of these designs have not reached the market due, at least in part, to problems associated with the expense of manufacturing, poor reliability or user acceptability. However, even though some of these designs operate poorly or are costly, they have still been commercialized due to the great need in hospitals or clinics for any type of safety syringe.
Most of the existing safety syringe designs allow for automatic retraction of the needle cannula into the plunger barrel of the syringe when the plunger is fully extended into the syringe. The automatic retraction is triggered when the plunger makes physical contact with the distal end of the syringe barrel. Typically, the end of the plunger is provided with a disengagable or sacrificial member at the distar end and the needle cannula is secured by a disengageable or sacrificial member. When the plunger reaches the fully extended position, the physical contact between the plunger and the needle cannula causes activation of the two respective disengageable or sacrificial members. In this manner, the end of the plunger barrel is opened and presented to receive the needle cannula. The needle cannula, no longer secured in position, is biased into the plunger barrel by a spring.
Conventional syringes are typically available in modular systems or kits in which approximately ten different sizes of syringes and approximately ten different sizes of needle cannulas can be used interchangeably. This allows an inventory of twenty items to be used in approximately 100 different combinations in accordance with the present need. However, the safety syringes presently available and described in the above patents are not modular and require stocking of an integral safety syringes for each combination of syringe size and needle cannula size desired, for example 100 different safety syringes. Particularly, in light of the greater cost of these syringes, the cost, distribution and storage of safety syringes is much greater than conventional syringes.
Despite the prevalence of modular conventional syringes, the emergence of a multitude of safety syringe designs and the increasing public outcry for safety syringes, the complexities of the safety syringe mechanisms have limited the number of attempts to design a safety syringe that is modular. Two such attempts include modular syringe tip designs that are combined with a conventional syringe as described in U.S. Pat. No. 5,891,093 (Dysarz) and U.S. Pat. No. 5,935,113 (Dysarz). Compared with the foregoing automatically retracting safety syringes, these two designs can be considered to have safety needle cannula assemblies that are self-contained and manually operated, while being connectable to a conventional syringe with a conventional locking arrangement. While these devices serve the aforementioned need for modularity, the obvious drawbacks to the devices include the manual retraction mechanism and the additional length that the needle cannula assembly adds to the syringe.
Therefore, there remains a need for a modular safety syringe system or kit that provides a selection of syringe modules having various sizes and 2 selection of needle cannula modules having various sizes that can be combined on site to form an automatically retractable safety syringe of a desired configuration. It would be desirable if the automatically retractable safety syringe had similar length and usability as a conventional syringe. It would be further desirable if the used automatically retractable safety syringe was compact and secure against accidental needle sticks.